I. Field of the Invention
This invention relates generally to surgical instruments for improving the outcome of percutaneous transluminal coronary angioplasty procedures, and more particularly to a catheter having a means for irradiating a treatment site with radiant energy, e.g., UV light, to reduce the incidences of restenosis.
II. Discussion of the Prior Art
Percutaneous transluminal coronary angioplasty (PTCA) has become a recognized method of reducing the occlusion of blood vessels due to coronary artery disease. The procedure involves routing a catheter having an inflatable balloon at the distal end thereof through the vascular system until the balloon is positioned at the site of the stenotic lesion to be treated. The balloon is then inflated to compress the atherosclerotic plaque into the wall of the coronary artery, thus increasing the size of the opening and enhancing blood flow through the affected artery. Approximately 400,000 angioplasty procedures are performed annually in the United States to open blocked coronary arteries. However, this successful procedure is overshadowed by the occurrence of restenosis, a re-narrowing of the artery. Studies have shown that 30-40 percent of angioplasty patients experience restenosis within six months of the angioplasty procedure. When restenosis occurs, patients may be treated with cardiovascular medications, additional angioplasty procedures or bypass surgery. Carrying out the angioplasty procedure results in damage to the endothelium and it is found that the body's natural response to such damage is a proliferation of smooth muscle cells, oftentimes resulting in restenosis.
In U.S. Pat. No. 5,053,033 to Richard H. Clarke, a technique is described for reducing incidences of restenosis following angioplasty. The patent describes a procedure in which the blood vessel walls at the angioplasty site are irradiated with UV light during the course of the angioplasty procedure and that the effect of such irradiation is to reduce proliferation of smooth muscle cells at the site of the damage. In accordance with the teachings of the Clarke patent, the UV radiation is delivered by means of an optical fiber incorporated into a percutaneous catheter. The UV radiation is sent down the optical fiber from a suitable laser or even a source of non-coherent UV light. It is theorized that ultraviolet light in the 240 nm to 280 nm range, when delivered to the DNA of smooth muscle cells effects cellular replication, thereby inhibiting proliferation.
In U.S. Pat. No. Reissue 34,544 to Spears, there is described a system for performing angioplasty which also uses light energy typically in the infrared range. In accordance with that patent, the subject is first injected with a hematoporphyrin which is selectively taken up into the atheromatous plaque. Subsequently, light in the IR range is made to impinge on the stenotic lesion, resulting in lysis of the plaque. A balloon catheter equipped with a flexible optical fiber is used to deliver the light to the source. When the balloon is inflated, it displaces the otherwise opaque blood allowing transmission of the IR energy through the balloon to the plaque being irradiated.
While research, to date, has been limited, medical scientists have been exploring the use of gamma radiation in treating damage to blood vessel walls resulting from angioplasty and/or atherectomy procedures.
Neither the Spears Reissue U.S. Pat. No. 34,544 nor the Clarke U.S. Pat. No. 5,053,033 teaches an apparatus for providing a uniform exposure of the intimal and endothelial layers at the site of the treated stenosis to radiation, such as UV light, over the entire area of the compressed lesion, nor precise control over the exposure time. Moreover, the liquid filled, hollow glass tube 24 at the distal end of the catheter 12 in the Spears patent would be relatively rigid and thus likely to cause damage to a vessel wall as the catheter carrying this structure is advanced through the vascular system. In the Clarke patent, the balloon 42 is deflated during the attempted exposure of the treated tissue to UV light. Hence, blood will surround the optical lens at the distal end of the catheter and effectively reduce the transmission of UV light to the tissue to be irradiated, thereby necessitating longer exposure times.
Thus, it can be seen from the foregoing a need exists for an improved instrument for exposing the area of compressed lesion to radiant energy in a controlled manner following balloon angioplasty so as to reduce the tendency toward smooth muscle growth and restenosis. It is a principal purpose of the present invention to satisfy this need.